a. Field of the Invention
The present invention relates to a molded article of fiber-reinforced thermoplastic which is light weight, has excellent mechanical strength, and can be utilized for various applications including automobile parts such as a bumper backup beam, door beam and seat shell, structural materials and machinery parts. The invention also relates to a process for preparing the material.
b. Description of the Prior Art
Fiber-reinforced thermoplastics (FRTP) are light weight and provide excellent mechanical strength. Hence, they are used in the form of molded articles for automobile parts, structural materials, machinery parts and other fields. The molded article is typically prepared by using a plate material essentially consisting of a thermoplastic resin and fibrous reinforcement as raw materials and by carrying out stamping and other molding processes.
In the stamping process, the plate material is heated above the melting temperature of the resin to provide fluidity for the plate material itself. Thereafter, the plate material is placed in a mold maintained at a temperature lower than the melting temperature of the resin, the mold is immediately closed, and cooling and forming are simultaneously carried out to obtain a molded article of an arbitrary form. The process, however, is liable to cause deformations or cracks in certain portions of the molded article particularly in the case of molding a complex shaped article. Consequently, restriction has been imposed upon the use of such materials.
Another process which has been tried, uses a sheet prepreg containing a unidirectionally arranged fiber, or a woven cloth impregnated with a thermoplastic resin, as a raw material of the molded article. However, a molded article prepared from the sheet prepreg cannot overcome the above problems of deformations and cracks, although strengths are generally higher than with articles prepared from the plate material. Additionally, the sheet prepreg is more expensive than the plate material. Constitution of the whole molded article with the sheet prepreg leads to higher production costs for the molded article.
In order to solve the problems of deformations and cracks, another process increases the overall strength of the molded article by selecting a specific resin and/or fibrous reinforcement for the plate material. For example, generation of deformations and cracks can be prevented by selection of high performance engineering plastics and/or carbon fiber. However, such plastics and fibrous reinforcement are very expensive. Consequently, it is unfavorable to prepare the whole molded article with such resin and fibrous reinforcement, because the portion required to prevent cracks and deformations is only a part of the molded article.